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How to Calculate Theoretical Yields

❶A mole is a tool used in chemistry to count molecules, based on their mass.   Start with a balanced chemical equation. A chemical equation describes the reactants on the left side reacting to form products on the right side. Some problems will give you this equation, while others ask you to write it out yourself, such as for a word problem. Since atoms are not created or destroyed during a chemical reaction, each element should have the same number of atoms on the left and right side. The equation is balanced. Read this guide if you are asked to balance an equation yourself.

Calculate the molar mass of each reactant. Look up the molar mass of each atom in the compound, then add them together to find the molar mass of that compound.

Do this for a single molecule of the compound. You can find a more precise value on a periodic table. Convert the amount of each reactant from grams to moles. Now it's time to look at the specific experiment you are studying. Write down the amounts of each reactant in grams.

Divide this value by that compound's molar mass to convert the amount to moles. Find the ratio of your reactions. A mole is an exact number for the amount of a substance and it is equal to 6. You now know how many molecules of each reactant you started with. Divide the moles of 1 reactant with the moles of the other to find the ratio of the 2 molecules.

You started with 1. The ratio of oxygen to glucose molecules is 1. This means you started with 9 molecules of oxygen for every 1 molecule of glucose. Find the ideal ratio for the reaction. Go back to the balanced equation you wrote down earlier. This balanced equation tells you the ideal ratio of molecules: The coefficients tell you there are 6 oxygen molecules and 1 glucose molecule.

Make sure you list the reactants in the same order you did for the other ratio. In a chemical reaction, 1 of the reactants gets used up before the others. The quantity of the product that is created in the reaction is limited by the reagent. Compare the 2 ratios you calculated to identify the limiting reactant: The bottom reactant in the ratio is the limiting reactant. If the actual ratio is smaller than the ideal ratio, you don't have enough of the top reactant, so it is the limiting reactant.

The bottom reactant, glucose, must be the limiting reactant. Identify your desired product. The right side of a chemical equation lists the products created by the reaction. Each product has a theoretical yield, meaning the amount of product you would expect to get if the reaction is perfectly efficient. The right-hand side lists 2 products, carbon dioxide and water. Write down the number of moles of your limiting reactant.

The theoretical yield of an experiment is the amount of product created in perfect conditions. To calculate this value, begin with the amount of limiting reactant in moles. This process is described above in the instructions for finding the limiting reactant.

In the example above, you discovered that glucose was the limiting reactant. You also calculated that you started with 0. Find the ratio of molecules in your product and reactant. Theoretical and Percent Yield. How to Calculate Theoretical Yields.

Depending on which text editor you're pasting into, you might have to add the italics to the site name. Steps in Finding Percent Yield. How to Calculate an Isolated Yield. How to Calculate Moles in a Reaction. Copyright Leaf Group Ltd. Multiply the ratio by the limiting reactant's quantity in moles. The answer is the theoretical yield, in moles, of the desired product.

In this example, the 25g of glucose equate to 0. The ratio of carbon dioxide to glucose is 6: You expect to create six times as many moles of carbon dioxide as you have of glucose to begin with. The theoretical yield of carbon dioxide is 0. Convert the result to grams. This is the reverse of your earlier step of calculating the number of moles or reactant.

When you know the number of moles that you expect, you will multiply by the molar mass of the product to find the theoretical yield in grams. The theoretical yield of the experiment is Repeat the calculation for the other product if desired.

In many experiments, you may only be concerned with the yield of one product. If you wish to find the theoretical yield of both products, just repeat the process. According to the balanced equation, you expect 6 molecules of water to come from 6 molecules of glucose. This is a ratio of 1: Therefore, beginning with 0.

Multiply the number of moles of water by the molar mass of water. Multiplying by the product, this results in 0. The theoretical yield of water for this experiment is 2. Doesn't one molecule of glucose produce six molecules of water, not one?

Not Helpful 0 Helpful 2. Your final step with the image you provided does not match. Is the theoretical mass of water 15 grams or 2. Answer this question Flag as Include your email address to get a message when this question is answered. Already answered Not a question Bad question Other. Quick Summary To calculate theoretical yield, start by finding the limiting reactant in the equation, which is the reactant that gets used up first when the chemical reaction takes place.

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Before performing chemical reactions, it is helpful to know how much product will be produced with given quantities of reactants. This is known as the theoretical yield. This is a strategy to use when calculating theoretical yield of a chemical reaction.

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To determine theoretical yield, multiply the amount of moles of the limiting reagent by the ratio of the limiting reagent and the synthesized product and by the molecular weight of the product.